The phone calls are not capable of being proved one way or the other. On the other hand the silencer and blood evidence can be proved by way of further forensic testing.
Jeremy is the one who needs to prove the phonecall happened. You seem to suffer from the delusion that a jury must accept Jeremy's claims as true unless there is 100% evidence to disprove it. This is patently false. A jury decides whether or not to believe the claims of a witness including a defendant.
I listed the various things that cut against Jeremy's claims being true. In the eyes of the law those reasons are more than sufficient to reject Jeremy's claim that the call happened.
In light of the fact that the shooting commenced in the bedroom with both parents being shot there and June being shot while she was still lying down in the bed it is crystal clear that the phone call didn't happen. Jeremy supporters can't come up with any plausible scenarios to account for June staying in bed and both parents being shot there together if Nevill phoned Jeremy for help. The few suggestions tossed out there were all pitiful.
Even setting aside the logistical issues there is not a plausible scenario where Nevill would call Jeremy to help. There is no reason why Jeremy would be summoned. By Jeremy's own admission he would have made matters worse not better. He had no calming effect over his sister. The only one known to have a calming effect was Nevill. In physical terms Nevill towered over Sheila and was very strong and had no need to ask Jeremy to come to disarm her. If he was panicked then time was of the essence and he would need to disarm her himself not wait for someone to dress and come. If she had the gun then walked out of the kitchen he would do everything in his power to follow and make sure she didn't harm his wife and grandkids. If too scared to follow and confront her without a weapon then upon her leaving he would have taken advantage of that opportunity to arm himself. The notion that right in front of her he grabbed the phone and called Jeremy as she was holding a weapon on him is ludicrous. The notion he called then she returned in the middle of the call and pushed the button down to disconnect the call is not the least bit credible. If she did that then she would have had only 1 hand on the weapon and have been too close to be able to point it at him with her other hand so would have been a prime opportunity to take it away from her. Nor is it credible that she hung up the phone then took it back off the hook and marched him upstairs at gunpoint to shoot them together.
Whether something seems credible or not plays a big role in whether to believe it happened.
There is no way to account for Sheila suddenly having a psychotic episode after going to bed and grabbing the gun and then waking up the family and June staying in her bed leaving the boys in their beds as Nevill tried to talk to her in the kitchen let alone for such to happen and in addition for Nevill to decided to call Jeremy to come to disarm her. It was a bad lie to make up. If Jeremy was known to have a calming effect on her then in that case saying he was called to come calm her down would have at least have been somewhat plausible.
